Devices for holding medical instruments in penetrating relationship with body tissue are known. See, for example, U.S. Pat. No. 2,256,942 which discloses an instrument having a fluted or undulated surface for retaining the device in the walls of the bladder or viscus; U.S. Pat. No. 3,750,667 which discloses a device having a thread which serves to measure the depth of introduction of the device into osseous tissue; and U.S. Pat. No. 4,670,008 which discloses a high flux threaded needle for injecting or removing fluids from the body, the needle having a threaded portion to permit easy insertion of the needle and secure the device in the patient.
Threaded structures have also been applied to larger diameter trocars which are used for introducing viewing and surgical instruments into the body. Such trocars are shown and described in U.S. Pat. Nos. 4,601,710; 4,654,030, and 4,902,280. One commercially available trocar includes an integrally molded threaded portion for holding the trocar in the patient's skin. Another device provides a depth penetration indicator adjustable to a desired position along a trocar and including a threaded portion for holding the trocar in the patient's skin.
The present invention provides an improved thread configuration for holding a medical instrument associated therewith in a desired position relative to a patient's body, specifically the patient's skin. The thread configuration of the present invention facilitates insertion and removal of the anchoring device into the patient's skin with decreased tissue trauma, and also provides sufficient holding power to maintain the medical instrument in the desired position.